Conventional disinfection and sterilization methods for medical instruments and disinfection methods for foods in packages and bags for foods include dry-heat sterilization, steam under pressure sterilization, radiosterilization, ethylene oxide gas sterilization and plasma sterilization.
Dry-heat sterilization uses high temperatures of 160 to 180° C. or above and this application is limited to metal and glass products. Sixty minutes are required to complete dry-heat sterilization. Steam under pressure sterilization also uses high temperatures and these applications are also limited to metal and glass products. Twenty minutes are required to complete steam under pressure sterilization. Moreover, this method cannot be used for humidity-sensitive materials (such as paper). Radiosterilization has the risk of a health hazard to the human body. Radiosterilization is not effective to areas where the radiation does not reach. Ethylene oxide gas sterilization requires very careful handling due to the toxicity and flammability of the gas used. The difficult disposal of residual materials after sterilization also poses a problem.
Various plasma sterilization techniques have been announced including, for example, the Publication of Unexamined Utility Model Application No. 57352-1994 and the Publication of Unexamined Patent Application No. 135571-2003. In principle, most of them use a high temperature to sterilize and as such involve handling problems. Some techniques use inert gases such as argon gas and chlorine gas in vacuum to generate gas plasma using a high-frequency power supply to sterilize the target objects. Chlorine gas is toxic and plasma occurs on the surface of the discharging electrode, and is not effective.
As described above, conventional plasma sterilization techniques use surface-wave plasma. The inside of a package is difficult to sterilize and as such sterilization is limited to the exterior of the package. These techniques are not applicable to resinous medical instruments such as catheters and injection devices and medical instruments that require sterilization of their insides such as vacuum tubes for drawing blood. The objects that can be sterilized are also limited due to thermal problems related to plasma irradiation. Other sterilization methods have various limitations and hazards due to their use of high temperature, high pressure and toxic gas. There has been a growing demand for a sterilization method that uses low temperature, low pressure and safe procedures and is capable of high-speed sterilization.